Genetic engineering of plants, which entails the isolation and manipulation of genetic material (usually in the form of DNA or RNA), and the subsequent introduction of that genetic material into plants or plant cells, offers considerable promise to modem agriculture and plant breeding. Increased crop values, higher yields, feed value, reduced production costs, pest resistance, stress tolerance, drought resistance, the production of pharmaceuticals, chemicals and biological molecules are all potentially available through genetic engineering techniques.
Methods for producing transgenic plants are well known. In a typical transformation scheme, a plant cell or plant tissue is transformed with a DNA construct, in which a “foreign” DNA molecule that is to be expressed in the plant cell or tissue is operably linked to a DNA promoter molecule, which will direct expression of the foreign DNA in the host cell, and to a 3′ regulatory region of DNA that will allow proper processing of the RNA transcribed from the foreign DNA. The choice of foreign DNA to be expressed will be based on the trait, or effect, desired for the transformed plant. The promoter molecule is selected so that the foreign DNA is expressed in the desired plant. Promoters are regulatory sequences that determine the time and place of gene expression. Transcription of DNA is dependent upon the presence of a promoter which is a DNA sequence that directs the binding of RNA polymerase and thereby promotes mRNA synthesis.
Currently, the most widely used promoter for expression of foreign gene constructs in dicot plants is the cauliflower mosaic virus (“CaMV”) 35S promoter (Ow et al., “Transient and Stable Expression of the Firefly Luciferase Gene in Plant Cells and Transgenic Plants,” Science 234:856-859 (1986)). The CaMV 35S promoter provides strong constitutive expression in most dicot plants, including cotton. Other promoters that are widely used for inducing the expression of heterologous genes in transgenic plants include the nopaline synthase (NOS) gene promoter from Agrobacterium tumefaciens (U.S. Pat. No. 5,034,322 to Rogers et al.), the CaMV 19S promoter (U.S. Pat. No. 5,352,605 to Fraley et al.), promoters derived from any of the several actin genes, which are known to be expressed in most plant cell types (U.S. Pat. No. 6,002,068 to Privalle et al.), and the ubiquitin promoter, which affords heterologous gene expression in many cell types.
However, to develop transgenic cottons with specialized agronomic traits such as fiber quality and seed nutrition components, a larger arsenal of constitutive and tissue-specific promoters will be required. The characteristic expression patterns provided by these promoters must be analyzed in order to determine if they can be used to express beneficial genes in specific target tissues or developmental stages at maximum levels. Although such promoter tests can be conducted with transient expression assays or in model plant systems such as transgenic tobacco and Arabidopsis, gene expression analysis in stable transgenic cotton plants provides confirmation that these promoters can be used for the development of commercial transgenic cotton. While several fiber-specific promoters have been identified or otherwise tested in transgenic cotton plants (John and Crow, “Gene Expression in Cotton (Gossypium hirsutum L) Fiber: Cloning of the mRNAs,” Proc. Natl. Acad. Sci. U.S.A. 89:5769-5773 (1992); Rinehart et al., “Tissue-specific and Developmental Regulation of Cotton Gene FbL2A,” Plant. Physiol. 112(3):1331-1341 (1996); Dang et al., “Expression of a Cotton Fiber Gene Promoter in Tobacco,” Proc. Beltwide Cotton Conf., San Antonio, Tex., Jan. 4-7, 1995 (Natl. Cotton Counc. Am., Memphis, Tenn.); Song et al., “Expression of a Promoter from a Fiber-specific Acyl Carrier Protein Gene in Transgenic Cotton Plants,” Proc. Beltwide Cotton Conf., San Diego, Calif., Jan. 5-9, 1998 (Natl. Cotton Counc. Am., Memphis, Tenn.), other tissue-specific promoters would be desirable to afford different expression characteristics for foreign genes in transgenic plants.
The present invention overcomes these and other deficiencies in the art.